The passion of the 31st round, "Low temperature is a GBB killer."
 
Some user test G5 in cold weather (around 10℃) and found that the power of shoot did not level down no matter semi or auto mode. It is accepted by everyone that G5 has good performance of gas efficiency.
 
In fact, the development of G5 use concept of GHK PDW started from two years ago; and the whole idea is around upgrading gas efficiency. But the test result could never reach the goal: it always failure after the 31st bullet shooting...

User may not know, there are lots of difficult conditions for M4. To achieve GHK standards, we still need to overcome many technical barriers. That's the reason why we do not have plan of M4 in few years ago. The plan of M4 is decided after the success of G5 theory.
 
The process of M4 development met lots of frustrations. Although we have foundation from G5, but it still has huge gap between two guns. In the earlier development of M4, it's easy to shoot away 40 rounds at one time by auto mode above 18℃. However, when the environment decrease to 10℃, we met a big trouble indeed. Through endless testing hell, we gave the birth of M4 finally.